Drawbench



May 10, 1966 G. A. MITCHELL 3,250,106

DRAWBENCH Original Filed May 17, 1963 I 2 Sheets-Sheet 1 FigJ mvemoa George AMifchell United States Patent Office 3,250,106 Patented May 10, 1966 DRAWBENCH George A. Mitchell, Youngstown, Ohio, assignor to Lombard Corporation, Youngstown, Ohio, a corporation of Ohio Original application May 17, 1963, Ser. No. 281,225, now Patent No. 3,216,234, dated Nov. 9, 1965. Divided and this application May 11, 1965, Ser. No. 454,871

- 4 Claims. (Cl. 72-291) The present application is a division of application Serial No. 281,225, filed May 17, 1963, which application is a continuation-in-part of application Serial No. 861,388, filed December 22, 1959, now abandoned.

This invention relates to drawbenches adapted to draw tubes and the like through a die, and more particularly to a drawbench of the type described in which the prime mover for the draw carriage is a fluid motor.

As is well known, a conventional chain drawbench employs, as a basic component, a circular die through which a tube is drawn in order to elongate the tube and reduce its diameter. In the usual drawing operation, the tube is first loaded onto a mandrel which extends parallel to the central axis of the die on one side thereof. The mandrel forwards a reduced diameter end of the tube into the die, and this end is engaged by gripper jaws carried on a draw carriage or'. dolly which travels on atrack extending parallel to the central axis of the die on the side opposite the mandrel. In operation, the draw carriage engages one or more continuously moving chains which force it along its track outwardly and away from the die, thereby pulling the tube through the annular opening defined between the periphery of the die and the periphery of the mandrel.

Although a drawbench of the type described above has won gneral acceptance and is useful in many applications, it has certain inherent disadvantages. In such benches the draw carriage is connected to the draw chain or chains by book devices which automatically retract when the carriage is not under tension. This arrangement is disadvantageous in the case of costly alloys where it is desired to stop the drawing operation before its completion to examine the progress of the drawn workpiece.

Another disadvantage of chain drawbenches resides in the fact that, as a practical matter, the maximum drawing force which they can achieve does not exceed about 300,000 pounds. Larger drawing forces would require extremely expensive and bulky draw chains, sprockets and associated gear drive apparatus. Furthermore, where the material being drawn is such that a single constant speed of the draw carriage cannot be tolerated, a chain drawbench, even one requiring a maximum drawing force below 300,000 pounds, requires a very expensive electrical control system to start and stop the draw chains. Still another disadvantage of chain benches is due to the fact that pulsations in drawing speed occur as the chain articulates over its drive sprocket. Such pulsations occur due to variations in the pitch diameter of the sprocket and produce undesirable effects on certain types of materials drawn on the bench. As the capacity of the bench increases, thus requiring a larger chain, this elfect is accentuated.

It is a primary object of this invention to provide a new and improved drawbench arrangement which overcomes the aforementioned disadvantages of conventional chain benches.

More specifically, an object of the invention is to provide a drawbench in which the motive force for the draw carriage is provided by an elongated hydraulic cylinder or fluid motor, and including means for positively supporting the piston means for the cylinder when said piston means is advanced out of the cylinder. In this respect,

the support means of the invention not only supports the piston means against gravity, but also prevents buckling of the same under the high drawing forces employed.

As will become apparent from the following detailed description, the invention includes a die stand having a mandrel-supporting structure and a track structure extending outwardly from its opposite sides and parallel to its central axis. Movable along the track structure is a draw carriage which, as in conventional drawbenches, engages the forward ends of tubes and pulls them through the die. In contrast to the usual drawbench arrangement, however, the draw carriage of the present invention is actuated by an elongated hydraulic cylinder which has a length substantially equal to, or slightly greater than, the maximum length of a tube which is to be drawn. Reciprocable within the cylinder is a piston which is connected at its forward end to the draw carriage, the arrangement being such that when the cylinder is pressurized, the piston is moved forwardly out of the cylinder to force the draw carriage away from the die. As will be understood, the length of the cylinder must be at least equal to the length of a drawn tube. This introduces problems in the design of the cylinder inasmuch as the weight of the piston assembly itself tends to cause it to bow downwardly along its length, and forces imparted tothe piston assembly tend to buckle it because of its great length. This is particularly true when the piston rod is exended out of its cylinder.

Accordingly, the present invention provides a means whereby the piston or piston rod may be supported along the length of the draw carriage track to prevent bowing or buckling of the same. This means comprises a C-shaped bushing means or cradle structure means which receives the rod as it advances along the track. In this respect, it is essential that the bushing means be less than a complete circle since otherwise it would be impossible to pass the piston rod through the bushing while at the same time have the draw carriage connected to the rod. On the other hand, the bushing means must encompass more than a 180 arc to prevent buckling of the rod under the high drawing forces employed.

The above and other objects and features of the invention will become apparent from the following detailed description taken in connection with the accompanying drawings which form a part of this specification and in which:

FIGURE 1 is a top view of the drawbench of the invention;

FIG. 2 is a side view of the drawbench shown in FIG. 1;

FIG. 3 is a cross-sectional view taken along line III.III of FIG. 1 showing a supporting frame section for the track structure of the drawbench shown in FIGS. 1 and 2;

FIG. 4 is an illustration of the hydraulic actuating cylinder for the drawbench of FIGS. 1 and 2, showing its length in comparison with its diameter; and

FIG. 5 is a cross-sectional view showing the construction of the hydraulic cylinder of FIG. 4.

Referring to FIG. 1, the numeral 10 designates a die stand having a die 12 therein. The die stand 10 is supported on a track assembly, generally indicated at. 14, which extends parallel to the central axis of the die on one side thereof. The track structure is comprisedof a plurality of spaced frame sections 16, an example of which is shown in FIG. 3. Each frame section comprises a pair of supporting members 18 and 20 which extend upwardly from a base 22'. The members 18 and 20 are interconnected by means of a steel plate 24 having an arcuate opening 26 provided in its central portion. Secured to the periphery of the arcuate opening 26 is a bronze liner or wear strip 28. The wear strips in the openings 26 of the several frame sections serve to guide and support the piston of an actuating hydraulic cylinder, hereinafter described, when it extends along the track structure 14.

Supported on the members 18 and 20 are a pair of tracks or guideways 30 and 32 which serve to guide a draw carriage 34 (FIGS. 1 and 2) along a path of travel which is in general alignment with the axis of die 12. The draw carriage 34 is provided with a pair of gripper jaws 36 which serve to engage the forward end of a tube inserted into the die 12. After the jaws 36 engage the end of a tube, the carriage 34 will be moved to the left as shown in FIGS. 1 and 2 to thereby pull the tube through the die in a manner hereinafter described.

To the right of die stand-10, as shown in FIGS. 1 and 2, is a mandrel supporting table or structure 33 which comprises an I-beam 40 or the like supported on a plurality of spaced structures 42, substantially as shown. Above the I-beam 40 is a trough 44 which supports the mandrel 46 and a tube carried thereby during a drawing operation. The right'end of structure 38, as shown in FIGS. 1 and 2, is provided with a mandrel manipulating mechanism which comprises a short stroke hydraulic cylinder 48 having its piston rod connected to a reciprocable actuating block 50. As shown, the block 50 is provided with a pair of guiding rods 52 and 54 slideable within bearings 56 which are welded or otherwise securely fastened to opposite sides of the I-beam 40. The mandrel 46 is pivotally connected to the upper portion of block 50 whereby the mandrel and the tube carried thereby may be moved to the left or right by actuating the cylinder 48. In operation, the cylinder 48 will-be initially pressurized to force the block 50 and mandrel 46 to the right as shown in FIGS. 1 and 2. Thereafter, the forward end of the mandrel 46 is elevated to the position shown in FIG. 2 where a tube from a tube storage rack, not shown, may be threaded onto the mandrel. The forward end of the tube is swaged or reduced in diameter such that the mandrel is lowered into a horizontal position, the cylinder 48 may be actuated to move the block 50 and the tube-carrying mandrel to the left. In this process the swaged or reduced diameter end of the tube is passed through the aperture formed by the die where it may be engaged by the gripper jaws 36 carried on draw carriage 34. The draw carriage is then forced to the left as shown in FIGS. 1 and 2 to thereby pull the tube blank through the die. The blank is thereby reduced to the dimensions of the annular opening between the periphery of the die and the periphery of the enlarged head 47 of the mandrel which extends into the die. Although a single mandrel and a single .die have been shown herein for purposes of simplicity, it should be understood that a plurality of mandrels and dies may be used if desired without departing from the scope of the invention. Actually, most drawbenches will incorporate a plurality of dies and mandrels rather than the single die arrangement illustrated in the drawings.

In order to force the draw carriage 34 to the left as shown in FIGS. 1 and 2, there is provided a fluid motor (FIGS. 4 and which comprises a hydraulic cylinder 58 having a ram-type piston 60 reciprocable therein. The cylinder 58 is carried by the mandrel supporting structure 38 and has a length at least equal to the maximum expected length of a tube which is to be drawn. In most cases this length will be approximately equal to that of the track structure 14 which, incidentally, is longer than the mandrel supporting structure 38. As the piston 60 moves forwardly out of the cylinder 58, it will pass through successive ones of the bushings 28 in the frame sections 16. Thus, the frame sections support the piston against gravity during a drawing operation. Otherwise, the weight of the piston might cause it to bow downwardly while it is in its fully extended position where the draw carriage 34 has moved to the left end of track structure 14. Note that the bushings 28 encompass more than 180 to prevent buckling of the rod under the high drawing forces employed. In other words, it is not enough to simply support the rod against gravity as by means of-spaced rollers. The fluid motor comprised of cylinder 58 and piston 60 is single acting, meaning that the piston 60 will move in a power stroke to the left only as shown in FIGS. 1 and 2. Movement of the piston to the left is accomplished by opening surge valve'62 at the right end of cylinder 58 which then connects the cylinder to a source of high fluid pressure, not shown. At the completion of a drawingoperation, the surge valve 62 is connected to a low pressure reservoir and means, not shown, such as a continuous chain, return the draw carriage 34 to its initial starting position where the cycle is repeated.

With the arrangement shown in FIGS. 1-3, extremely high drawing forces, on the order of one million pounds or over, can be achieved. Furthermore, the speed of the draw carriage 34 can be made infinitely variable by merely regulating the variable volume pumps, not shown, which supply fluid under pressure to the cylinder. Thus, the apparatus can easily accommodate tubes of various materials which require differentdrawing speeds. The drawing operation may be stopped and again started by merely shutting valve 62 after drawing has initially started. All of the foregoing advantages are, of course, unobtainable in conventional chain type benches as was explained above.

In FIG. 4 the length of cylinder 58 as compared with its diameter is shown where the length of the cylinder is many times its diameter. The cylinder is formed from three sections A, B and C which comprises sections of pipe having flanged ends bolted together as at 64 and 66. In FIG. 5 it can be seen that the left end of the cylinder 58 is provided-With a sealing head which comprises a generally annular member 68 connected by means of bolts 70 to a flange 72 on section A of the cylinder. The annular member 68 is provided with a circular recess 74 which carries -a packing ring 76 and annular bushing 78 of bronze or some other similar metal. The end of annular member 68 is provided with and end plate 80 which is connected to the annular member 68 by means of bolts 82. A small wiping seal 84 is provided in a recess 85 formed in the end plate 80, substantially as shown.

The ends of sections A nd B which are bolted together at 64 are bored as at 86 and 88 to provide a recess in the inner periphery of the cylinder 58. Received within this recess is an annular bronze bushing 90, it being understood that a similar bronze bushing is provided at junction 66 between sections B and C. Between bushings 90 and annular member 68 is a second bronze bushing 92 which is slideably positioned within the cylinder. This latter bushing does not fit within a recess and has an outer circumference substantially coincident with theinner circumference of the cylinder 58. One or more of the bushings 92 may be provided between annular member 68 and bushing 90, or between junctions 64 and 66. To restrain the bushing 92 against axial movement, a pair of cylindrical spacers 94 and 96 are provided. These spacers are loosely fitted within the cylinder to permit thermal expansion 'of the various parts.

The inner diameters of bushings 78, 90 and 92 are all equal. These bushings receive the piston 60 which is a tubular member having circular plugs 98 provided at its opposite ends. When the right end of cylinder 58 is pressurized, the piston 60 will be forced to the left as shown in FIG. 2. In so doing, it rides on the inner peripheries of the bushings 78, 90, 92, etc. Thus, this piston 60 will make contact with the sides of the cylinder at spaced points only, these points being at the bushings 78, 90, 92, etc. As will be understood, only the various bushings 78, 90, 92 etc. need be machined since they are the only members which make contact with the sliding piston 60. Generally speaking, the arrangement shown above is practical whenever the length of the cylinder is at least thirty times its diameter and can be extended to almost any length within reason.

The invention thus provides a drawbench which may be actuated by a hydraulic cylinder and piston arrangement. Although the invention has been shown in connection with a certain specific embodiment, it will be readily apparent to those skilled in the art that various changes in form and arrangement of parts may be made to suit requirements without departing from the spirit and scope of the invention. In this respect, it should be apparent that the invention is applicable to bar drawbenches as well as those in which the workpiece is a tubular member. In addition, two or more cylinders may be used on either side of the draw carriage rather than the single arrangement shown herein which requires a cantilever connection between the driving force and the carriage.

I claim as my invention:

1. In a drawbench including a drawing die, a track structure extending parallel to the axis of said die on one side thereof, and a draw carriage movable along said track structure for pulling workpieces through said die; the improvement which comprises a hydraulic cylinder extending parallel to the central axis of said die on one side thereof opposite said track structure, an elongated piston slideable within said cylinder and movable from a position within the cylinder to a position where it extends along the length of said track structure, means connecting said piston to said draw carriage whereby the carriage will be forced to move away from the die when the piston advances out of the cylinder, and cradle structure means adjacent said track structure for supporting said piston as it moves outwardly from the cylinder, said cradle structure means including arcuate, stationary bushing means for receiving said piston, the bushing means being generally C-shaped in cross-sectional configuration and having a radius slightly larger than the radius of said piston, said bushing means extending through an are greater than 180 but less than 360 to define an opening through which the connecting means between the piston and draw carriage may pass when the draw carriage is forced away from the die, whereby buckling of the piston under compressive forces during a drawing operation is eliminated.

2. In a drawbench including a drawing die, a track structure extending parallel to the axis of said die on one side thereof, and a draw carriage movable along said track structure for pulling workpieces through said die; the improvement which comprises a hydraulic cylinder extending parallel to the central axis of said die on the side thereof opposite said track structure, an elongated piston slideable within said cylinder and movable from a position within the cylinder to a position where it extends along the length of said track structure, means connecting the piston to said draw carriage whereby the carriage will be g forced to move away from the die when the piston advances out of the cylinder, and a plurality of cradle structures spaced along said track structure for supporting said piston as it moves outwardly from the cylinder, the cradle structures each including an arcuate, stationary bushing for receiving said piston, each bushing being generally C-shaped in configuration and having a radius slightly larger than the radius of said piston, each of said bushings extending through an are greater than 180 but less than 360 to define an opening through which the connecting means between the piston and draw carriage may pass as the draw carriage is forced away from the die, whereby buckling of the piston under compressive forces during a drawing operation is eliminated.-

3. In a drawbench including a drawing die, a track structure extending parallel to the axis of said die on one side thereof, and a draw carriage movable along said track structure for pulling workpieces through said die; the improvement which comprises a hydraulic cylinder extending parallel to the central axis of said die on the side thereof opposite said track structure, an elongated piston slideable within said cylinder and movable from a position within the cylinder to a position where it extends along the length of said track structure, means connecting said piston to said draw carriage whereby the carriage will be forced to move away from the die when the piston advances out of the cylinder, and generally C-shaped stationary support'means positioned adjacent said track structure for supporting the piston against gravity when it moves outwardly from the cylinder, sa'id C-shaped support means having a radius slightly larger than the radius of said piston and an axis coaxial with the axis of said piston whereby the piston will slide into the C-shaped support means as it moves out of its cylinder during a drawing operation, the C-shaped support means defining an are greater than 180 but less than 360 in cross section to define an opening through which the connection means between the piston and draw carriage may pass when the draw carriage is forced away from the die, whereby buckling of the piston during a drawing operation is eliminated.

4. The improvement of claim 3 wherein the piston is of the ram-type and has a length substantially equal to the length of said cylinder, and wherein the forward end of the piston is connected to said draw carriage.

References Cited by the Examiner UNITED STATES PATENTS 531,723 1/1895 Hill 3086 587,360 7/1897 Carroll 91-168 2,365,680 12/1944 Curtis 97 3,173,284 3/1965 Bean 72-283 RICHARD J. HERBST, Primary Examiner.

CHARLES W. LANHAM, Examiner. H. D. HOINKES, Assistant Examiner. 

1. IN A DRAWBENCH INCLUDING A DRAWING DIE, A TRACK STRUCTURE EXTENDING PARALLEL TO THE AXIS OF SAID DIE ON ONE SIDE THEREOF, AND A DRAW CARRIAGE MOVABLE ALONG SAID TRACK STRUCTURE FOR PULLING WORKPIECES THROUGH SAID DIE; THE IMPROVEMENT WHICH COMPRISES A HYDRAULIC CYLINDER EXTENDING PARALLEL TO THE CENTRAL AXIS OF SAID DIE ON ONE SIDE THEREOF OPPOSITE SAID TRACK STRUCTURE, AN ELONGATED PISTON SLIDEABLE WITHIN SAID CYLINDER AND MOVABLE FROM A POSITION WITHIN THE CYLINDER TO A POSITION WHERE IT EXTENDS ALONG THE LENGTH OF SAID TRACK STRUTURE, MEANS CONNECTING SAID PISTON TO SAID DRAW CARRIAGE WHEREBY THE CARRIAGE WILL BE FORCED TO MOVE AWAY FROM THE DIE WHEN THE PISTON ADVANCES OUT OF THE CYLINDER, AND CRADLE STRUCTURE MEANS ADJACENT SAID TRACK STRUCTURE FOR SUPPORTING SAID PISTON AS IT MOVES OUTWARDLY FROM THE CYLINDER, SAID CRADLE STRUCTURE MEANS INCLUDING ARCUATE, STATIONARY BUSHING MEANS FOR RECEIVING SAID PISTON, THE BUSHING MEANS BEING GENERALLY C-SHAPED IN CROSS-SECTIONAL CONFIGURATION AND HAVING A RADIUS SLIGHTLY LARGER THAN THE RADIUS OF SAID PISTON, SAID BUSHING MEANS EXTENDING THROUGH AN ARC GREATER THAN 180* BUT LESS THAN 360* TO DEFINE AN OPENING THROUGH WHICH THE CONNECTING MEANS BETWEEN THE PISTON AND DRAW CARRIAGE MAY PASS WHEN THE DRAW CARRIAGE IS FORCED AWAY FROM THE DIE, WHEREBY BUCKLING OF THE PISTON UNDER COMPRESSIVE FORCES DURING A DRAWING OPERATION IS ELIMINATED. 